Electrochemical sensor instruments can detect and quantify chemicals in fluids without the use of radioactive materials and, in contrast to colorimetric methods, even in the presence of color and/or turbidity. The general principle is to construct a sensor with an electroactive sensing element, one whose electroconductivity changes in response to the presence of the analyte of interest, either because the sensing element combines with the analyte or because the sensing element combines with a reaction product whose concentration is affected by the presence of the analyte.
It is advantageous for the electrochemical sensor instrument to have two separate components: a cartridge and an electronic instrumentation unit. The cartridge will have one or more cells for receiving fluid samples, an electroactive sensing element in each cell, and an electrical connection that, when the cartridge is placed in the instrumentation unit, connects the electroactive sensing element to the instrumentation unit.
Optimal use of sensors for environmental, agricultural, or medical diagnostic purposes requires that they meet minimum standards of accuracy and precision. Quantitative analysis involves a comparison between the electrical changes caused by the test sample and the electrical changes caused by at least one standard, such as a sample with known analyte concentration. Nevertheless, limitations on accuracy and precision occur in such comparisons. Sources of such variation include fluctuations in electroactive sensing element composition and dimensions that are inherent in the electrode manufacturing process. The present inventions deal with improvements in electrochemical sensor design that help to minimize the effects of such variations.